When a stage adaptation of a pre-existing work fizzles, it's typically because it hasn't adequately captured the spirit or the necessity of its source. Whether or not it's otherwise faithful to the original is usually an academic concern. With Sister Act, the new musical incarnation of the 1992 Hollywood comedy that just opened at the Broadway, the problem runs deeper. So much is the same, and yet so much is different about Alan Menken, Glenn Slater, Cheri and Bill Steinkellner, and Douglas Carter Beane's musical compared to the hit Whoopi Goldberg screen vehicle that it's impossible to tell whether the adapters had any affectionor planfor it at all.

In case the plot needs recounting, here goes. A hardscrabble singer named Deloris Van Cartier witnesses her mobster boyfriend's gang commit a murder. She runs to the police and agrees to testify, but they can't get a trial any time soon. So the police put her in the last place anyone would look for someone of her easy virtue: a struggling nun's collective. Forced by the authoritarian Mother Superior to dress in a habit and obey strict Catholic edicts, Deloris initially rebels but eventually finds her inner Carmelite by helping her down-on-their-luck sisters turn their beleaguered choir into a popular, money-raising sensation.

These basic precepts remain in the Steinkellners' book (for which Beane has provided additional material), but nearly all the details have changedvery few of them for the better.

It's no longer 1992, but 1977-1978. Deloris (here played by Patina Miller) has morphed from Reno casino entertainment, hanging on only because of her boyfriend's largess, into a trying-to-make-it gold-digger in Philadelphia hoping to use Curtis (Kingsley Leggs) to kick-start her career. Whereas the movie presented a powerful and sympathetic police lieutenant, Eddie Souther, as Deloris's protector, onstage he's a bumbling officer who can barely raise a gun, and doesn't know how to do his job. (Chester Gregory plays him.) When sweaty Eddie, as he's consistently mocked, hides Deloris, he moves her to a church in town, rather than hundreds of miles away as in the moviesomething that makes it easier for Curtis and his boys to track down Deloris, which of course happens early on in the first act.

Victoria Clark and Patina Miller.Photo by Joan Marcus.

This defuses any and all tension, yet the show stumbles on. The Mother Superior (Victoria Clark) is now a tart discontent whose beliefs are grounded in self-concerned prejudices rather than an internal clash of Vatican I conservatism with Vatican II liberalness. Yet, unlike the movie, where Deloris merely pulled the spirituality out of girl-group numbers like "My Guy" and "I Will Follow to Him" to create upbeat modern hymns, in the musical she makes everything she touches profane and flashy. She even outfits the presiding monsignor (Fred Applegate) and the chancel's towering statue of the Virgin Mary in acres of silver lamé and enough sequins to send Liberace spinning in his grave. (The costume designer is Lez Brotherston.)

The movie charmed for three reasons, all of which the musical obliterates: the gentle but serious tension between the Mother Superior and Deloris, both of whom wanted only the best for the convent; Deloris's relationship with two smart but troubled nuns, Mary Robert and Mary Patrick, whom she elevated to richer sense of self; and an abiding respect for the benefits religion can bring to both individuals and society. With everything reduced to flat, musical-comedy-winking insouciance (seriously, hyperkinetic 40-year-old altar boys?), and nothing treated as if it matters to anyone (and with toenail-deep direction from Jerry Zaks to match), this is Sister Act: Las Vegas through and through.

This is not to say everything is cheesy. Klara Zieglerova's sets establish a nice contrast between the classically holy church, complete with stained glass and flying buttresses, and the sleaziness of everyday life; and Natasha Katz's lights maintain marginal restraint. Menken, of course, is both a gifted Disney melodist (for both Beauty and the Beast and The Little Mermaid) and a prime pastiche artist (Little Shop of Horrors), and his music is as foot-tapping and catchy as any Broadway has heard this season. Deloris's first number, Take Me to Heaven, starts the evening off on a close-harmony high, and if nothing else quite matches it, the tunes (as orchestrated by Doug Besterman) never get tiring as they parade through every nook and cranny of the '70s jukebox.

But the parade of styles in which the compositions march does, with Temptations-style harmony, Barry White slithering, and various other funk, soul, and R&B retreads substituting for true character sounds, something that hamstrings Slater's polished but unremarkable lyrics. (Anthony Van Laast's choreography, often ripping off Solid Gold and its myriad imitators, is also a pale imitation of useful theatre dance.) The cumulative effect of all this is that of watching a Fringe Festival parody of an authentic musical, one that samples earnestness only because it thinks jokes about it will be funnier later.

The performances, all professional but pointless, don't stand a chance. Miller is a dynamo, to be sure, and a far superior singer to Goldberg (who, incidentally, is a producer of the musical), but her blaring line deliveries and constantly arched eyebrows suggest she's viewing Deloris's every action from a mile away, something that makes her neither graceful nor likeable. Gregory and Applegate are so hampered by the buffooning up of Eddie and O'Hara that they never come across as even two-dimensional. Leggs brings plenty of suave smoothness to Curtis, but the role, less threatening than Harvey Keitel's in the movie, gives him no real opportunities. Mary Robert and Mary Patrick, chopped down to bit parts, do no favors for the ostensibly talented actresses playing them, Marla Mindelle and Sarah Bolt.

Clark alone rises above her writing's mediocrity, not erasing memories of Maggie Smith in the film, but creating a woman of her own specific problems. If it's difficult to fully accept Clark's Mother Superior as both loving and deeply conflicted, rather than just annoyed at Deloris's antics, the actress radiates enough warmth of her own to fill the gaps.

Everything else, however, is Antarctic cold, so much so that you may wonder whether you're watching a cavalcade of trained penguins rather than actresses dressed up a nuns. The ultimate effect isn't merely to send you back to the far superior film, though the musical will do that, but to make you realize that miracles can happen after all. What else can explain how, in comparison to Sister Act, Nunsense seems the height of honesty, nuance, and sophistication?